Battery packs including a plurality of batteries accommodated in a case to allow an output of a predetermined voltage and capacitance are widely used as power sources of various devices, vehicles, etc. Specifically, the technique of forming modules of battery assemblies obtained by connecting general-purpose batteries in parallel and/or in series to output a predetermined voltage and capacitance, and combining the battery modules together to be applicable to various applications is beginning to be used. This module forming technique can reduce the size and weight of the battery modules themselves by increasing the performance of batteries accommodated in the battery modules. Thus, this module forming technique has various advantages, an example of which is that workability can be improved in assembling a battery pack, and the flexibility in mounting the battery module in areas of limited space, such as a vehicle, can be increased.
However, the performance of the batteries included in each battery assembly is not necessarily uniform. Therefore, for example, during discharge, the current capacity of the battery assembly is limited by a battery having a minimum capacity, and during charge, recharging the whole battery assembly is limited by the battery having the minimum capacity. Thus, when the battery assembly is charged and discharged beyond such limits, problems such as a reduction in cycle life of the battery assembly may arise due to deterioration of the battery having the minimum capacity.
As a method to solve such problems, Patent Document 1 describes that in a battery assembly including a plurality of batteries connected to each other in parallel and/or in series, adjacent batteries are connected to each other in a complex manner to configure a network. When such a network is configured, batteries having non-uniform properties are automatically equilibrated, so that it is possible to reduce performance degradation of a certain battery, as a result of which the cycle life of the battery assembly can be extended.